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copper ;  the impurities may, if required, be estimated as in commercial
copper (see p. 215).

1.  Determination  of the Silicon.—i gram of the finely powdered
sample is treated with 10-20 c.c. of nitric acid (D 1-4) and heated for a
long time.   After addition of 1-2 c.c. of hydrochloric acid, it is again heated
for a short time and finally evaporated in presence of 2 c.c. of sulphuric
acid.   The heating is continued on a sand-bath until copious white fumes
of sulphuric acid are emitted, the cooled residue being treated with hot
water, filtered, and the filter thoroughly washed with hot water acidified
with sulphuric acid.   The filter, still somewhat moist, is placed point
upwards in a platinum crucible and the latter covered and heated, at first
gently and later to ignition, the subsequent procedure being that followed
in estimating silicon in iron or steel (see p. 171).

2.  Determination  of the Copper.—The filtrate from the silica is
acidified with 5-6 c.c. of nitric acid, made up to 250-300 c.c. and electrolysed
to determine the copper.    Winlder electrodes ;   ND100 = 0-3-0-4 amp. ;
duration, 10-15 hours.

The commoner commercial types of cupro-silicon contain 10, 15, 20 and 35°/
of silicon.                                                                                                       °


The copper-manganese alloys are used as deoxidisers of copper, and
for the preparation of copper-manganese alloys with a low content of man-
ganese—so-called manganese bronzes—and of the manganese brasses and
true manganese bronzes. Analysis includes determination of the copper
and manganese and, sometimes, of the impurities, particularly the silicon,
lead, iron and nickel.

1, Determination of the Copper.—i gram of the sample is treated
in a covered dish with 10-15 c.c. of nitric acid (D 1-2), 6 c.c. of dilute sul-
phuric acid (i vol. acid to i vol. water) being added when the action is
complete and the liquid evaporated on a water-bath to eliminate the nitric
acid and then heated on a sand-bath until copious white fumes of sulphuric
acid appear. When cool, the residue is stirred and gently heated with
30 c.c. of water to dissolve the copper and manganese sulphates, 5 c.c. of
95% alcohol being added and the mixture left for one or two hours. Any
insoluble residue, consisting usually of silica and lead sulphate, is filtered
off and washed with a mixture of 60 c.c. of water, 10 e.c. of alcohol and 0-5
c.c. of sulphuric acid, the filtrate being evaporated almost to dryness to
expel all the alcohol, and the residue taken up in water, diluted to 150 c.c.,
heated to 60-70° and electrolysed to determine the copper : Winkler elec-
trodes ; temperature = 60-70°; ND100 = 0-2-0-3 amP- > duration =
6-7 hours.

When the whole of the copper is deposited the solution is allowed to
cool a little, the cover-glasses removed from the beaker, the latter slowly
lowered and the electrodes washed with water as they emerge. The cathode
is then washed with water, alcohol and ether, dried at 70° and weighed.es the tenacity